Numerical Simulation Of Aircraft Wake Vortex Under Typical Weather Conditions

Aircraft wake is a byproduct of wing lift.The pressure difference between the upper and lower surfaces of the wing causes the air flow from the lower surface around the wing tip to the upper surface.After leaving the trailing edge of the wing tip,the free vortex surface will roll up to form a pair of counter-rotating vortices of equal intensity,thereby forming the aircraft wake.Aircraft wake is an important factor that affects flight safety and restricts the growth of airspace capacity in the terminal area.In recent years,ICAO,FAA,etc.have conducted systematic and in-depth research on the evolution mechanism of aircraft wake,and found that Turbulence intensity,temperature,crosswind and other weather conditions have important effects on wake dissipation.In this thesis,the large eddy simulation model is used to systematically study the effects of different weather conditions such as turbulence intensity,temperature,crosswind,and water mist on the evolution of aircraft wake vortices during the near-ground take-off stage.From the perspectives of wake vortex intensity dissipation characteristics,wake vortex horizontal motion and vertical motion characteristics,etc.,to discuss the physical mechanism of the influence of various weather conditions.At the same time,according to the calculation results of numerical simulation,the safety and feasibility of reducing the wake separation between ARJ21 aircraft and A330-200 aircraft under different weather conditions are studied with ARJ21 aircraft as the rear aircraft.The research shows that the larger the turbulence intensity is,the faster the wake vortex dissipates,and the turbulence intensity mainly affects the time when the wake vortex enters the fast dissipation stage;This is because atmospheric turbulence enhances the flow exchange between the wake vortex and the atmosphere,forming a secondary vortex structure wrapped around the wake vortex,increasing the instability of the wake vortex;The effect of different turbulence intensities on the wake vortex motion is basically the same;The vortex core spacing decreases in the initial stage,because the trailing edge vortex surface of the wing merges into the wingtip vortex and rolls up to form a new vortex core,which is closer to the aircraft of symmetry;As the radius of the wake vortex increases,the interaction between the left and right vortices increases,and the distance between the vortex cores increases gradually.The larger the rate of vertical temperature decrement is,the faster the wake vortex dissipation will be,because the temperature gradient enhances the instability of the flow field,resulting in a faster decay of the wake vortex intensity;The effects of different rate of vertical temperature decrement on the vortex core spacing and wake vortex height are different;Before 't =2,the distance between vortex cores gradually decreases under different rate of vertical temperature decrement,and then gradually increases under negative rate of vertical temperature decrement,and continues to decrease under positive rate of vertical temperature decrement;Different rate of vertical temperature decrement will lead to the acceleration of the decline rate of the wake vortex,and the greater the absolute rate of vertical temperature decrement,the faster the decline rate of the wake vortex.The crosswind will accelerate the attenuation of the wake vortex intensity.The larger the crosswind,the faster the wake vortex intensity attenuation;The crosswind also causes the asymmetry of the attenuation of the left and right vortices.In the initial stage,the left vortex(upwind vortex)decays faster,and then the right vortex(downwind vortex)decays faster than the left vortex;.The larger the crosswind,the faster the wake vortex intensity attenuation.In a small crosswind environment,the wake vortex dissipation still has two stages of initial dissipation and rapid dissipation.When the crosswind is large,the wake vortex will enter the fast dissipation stage in a very short time.The crosswind also causes the asymmetry of the attenuation of the left and right vortices.In the initial stage,the left vortex(upwind vortex)decays faster,and then the right vortex(downwind vortex)decays faster than the left vortex.The crosswind has a great influence on the movement of the wake vortex;First,the crosswind will cause the overall lateral displacement of the wake vortex,and the displacement becomes more obvious as the wind speed increases;The crosswind also causes the asymmetry of the left and right vortex motion;In the initial stage,the upwind vortex moves faster laterally,and the lateral motion of the downwind vortex will be larger than that of the upwind vortex over time;In addition,the crosswind will also cause the inconsistency of the descending height of the left and right vortices;Especially when the crosswind is 7m/s,the left vortex is affected by the right vortex,and the descending height is significantly reduced.The existence of water mist will accelerate the dissipation of the wake vortex;This is because of the drag effect between the raindrops and the airflow in the wake vortex area;The greater the rainfall,the stronger the drag effect and the faster the attenuation of the wake vortex intensity;The water fog condition has a great influence on the vertical motion of the wake vortex,and the descending speed of the wake vortex will be faster with the increase of rainfall,because the drag effect of raindrops on the wake vortex will increase with the increase of rainfall.By analyzing the response and safety of ARJ21 aircraft encountering A330-200 aircraft wake under different weather conditions.It is found that when ARJ21 encounters wake at the take-off wake separation for Category F aircraft(120s)stipulated by ICAO,the overload increment is less than 0.15,that is,it is in a no-turbulence state,and the maximum rolling moment coefficient is less than 0.048.According to the limit rolling moment coefficient of experimental value and theoretical value,this thesis calculates the minimum time separation when ARJ21 follows A330-200 to take off under different weather conditions.Compared with the wake separation(120s)specified by ICAO,the results calculated in this thesis can be shortened by about 5 seconds to 30 seconds.